[TowerTalk] Stacking Distances

I am a true advocate of 0.5 wl stacking in most of the practical situations.
In real life the limiting factor for you is usually the height of the tower
or the height of the upper antenna. So when we are talking about stacking
distance we are talking about the height of the lower antenna.
The inlfuence of the stacking distance is growing with the boomlength of the
antennas. For 3 element yagis the distance is not so critical. For 6 element
OWAs I have found either 1 wl or 0.5wl be appropriate. The only advantage
for 1 wl is a marginal increase in gain if at all, all the other factors are
for 0.5wl:
-clean pattern (0.5 minimizes the unwanted lobe, not 5/8)
-lower antenna is higher, less obstructions on ground, less RF
-mechanically easier to mount on the same mast and takes less tower space
-you can mount 3rd antenna at 1 wl and get a horrible killer stack!
All the 0.5wl stacks I have tested show incredible performance gainwise and
patternwise (2x6el owas at 15 and 10meters, 2x3el on 40m)
In conclusion - whenever the upper antenna is not higher than 2wl I would
never doubt a second to choose 0.5wl stacking, when higher then you might
think about it and model it. There is no point in looking at best stacking
distance in free space as we never get that high:)
73
tonno
es5tv
----- Original Message -----
From: "Pete Smith" <n4zr@contesting.com>
To: "Paul Christensen, Esq." <w9ac@arrl.net>; "Tower"
<towertalk@contesting.com>
Sent: Thursday, May 22, 2003 4:15 PM
Subject: Re: [TowerTalk] Stacking Distances
> At 08:50 AM 5/22/03 -0400, Paul Christensen, Esq. wrote:
> >Question: Is 5/8-wave used as a compromise spread in that the difference
> >between 1 w.l. and 5/8 w.l. is relatively small but closer than 5/8 w.l.
> >produces quickly diminishing forward gain? Or, is there a benefit of 5/8
> >w.l. that minimizes an unwanted lobe?
>
>
> Here's a table of gain, take-off angle and F/B versus stacking distance
for
> 6-element OWA 20M yagis, as computed by NEC-2. In all cases, I used the
> 1X/2X rule -- a classic choice for cancellation of the second forward
> lobe. So If Ht = 40 feet, then the stack is at 40/80 feet, and so
> on. It's fairly intriguing that the best combination of F/R and gain
> happens at 90/180. Presumably this setup is not much used because the
> take-off angle is too low for Europe (at least from the East Coast). I
> haven't looked at how these characteristics vary across the band at the
> various spacings, but I wouldn't be surprised if the "sharpness" of the
max
> gain and max SWR points within the band varied considerably.
>
> Freq Ht R X SWR Gain TOA F/R
> 14.200 40 26.82 1.64 1.867 16.34 14 20.74
> 14.200 45 26.75 2.04 1.873 16.73 12 20.01
> 14.200 50 27.71 2.40 1.810 16.99 11 18.76
> 14.200 55 28.84 0.91 1.735 17.25 10 16.32
> 14.200 60 28.02 -0.54 1.785 17.53 9 17.10
> 14.200 65 26.98 -0.87 1.854 17.72 9 18.37
> 14.200 70 26.28 -0.73 1.903 17.81 8 19.33
> 14.200 75 25.86 -0.44 1.934 17.81 8 19.45
> 14.200 80 25.65 -0.12 1.949 17.82 7 17.76
> 14.200 85 25.66 0.18 1.949 17.83 7 18.99
> 14.200 90 25.76 0.22 1.941 17.81 6 20.74
>
> 73, Pete N4ZR
> The World HF Contest Station Database was updated 9 May 03.
> Are you current? www.pvrc.org/wcsd/wcsdsearch.htm
>
>
>
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